Thank you Jon and Nicholas. I already have "console=ttyS0" in the kernel command line. That is not helping me.
I looked at the major/minor numbers with a good working system and it looks correct for the nodes created in ramdisk. What is the kernel routine that is first called when there is, for example a read() function call from user program? I would like to start debugging from there and see if any thing at all happens when there is a call. Appreciate your help with this question. Thanks Siva -----Original Message----- From: Nicholas Mc Guire [mailto:[EMAIL PROTECTED] Sent: Friday, December 28, 2007 12:39 AM To: Siva Prasad Cc: linuxppc-dev@ozlabs.org; [EMAIL PROTECTED] Subject: Re: Device node - How does kernel know about it -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 > * Ramdisk is also executing fine, just that prints are not coming out of > serial. I can see the execution of various user programs with a printk > in sys_execve() routine. Ramdisk has all the required files like > /dev/console, /dev/ttyS0, etc. > * Looking further into tty driver, I noticed that call to tty_write() or > do_tty_write() is not happening at all. So, somewhere the interface > between kernel and user program is lost. > * Just to check it out, I tried to write a small kernel module and a > test program. > - Attached memtest.c module (not really testing memory there. :-)) > - Attached testmemtest.c user program, that just open's it and reads > the information > - Created a device node using "mknod /dev/memtest c 168 0" > - When I do "insmod memtest.ko" inside the ramdisk bootup scripts, I > could see all the printk's on the console > - When I execute "testmemtest" next in the same script, it does not > display the printk inside of memtest.c module. This only indicates that > read call did not really go to the kernel side. > - Just to check my program's validity, I checked on a similar machine > and all the code works fine. > - "uname -r" also matches with what I built. So, chances of exiting > from open call because of mismatch is remote. Since userland cannot > print, I have no idea what exactly is happening there. > The kernel will simply look at the major:minor numbers - so maybe you simply have a wrong major/minor for /dev/ttyS0 ? in that case you will see nothing but other than that most things will go on working. hofrat -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFHdLY2nU7rXZKfY2oRApFpAKCKfGanKHGuFFJmUFy3aQtjmWNjEACfU7uK hrfpn2RMn5l23ZqCOXV5rd8= =GfsF -----END PGP SIGNATURE----- _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev